Wave-guide transitions



P 1955 R. M. WALKER 2,706,278

WAVE-GUIDE TRANSITIONS Filed July 19, 1948 IN V EN TOR.

Richard M Waller B WK 1 M4.

United States Patent WAVE-GUIDE TRAN SITIONS Richard M. Walker, Dorchester, Mass., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application July 19, 1948, Serial No. 39,496

16 Claims. (Cl. 333-98) The present invention relates to ultra high frequency radio transmission by means of wave-guides.

The circular wave-guide operating in the transverse electric mode TEoi is notably efficient, in respect to low loss for a given wave-guide size. An objection limiting the use of the circular wave-guide is the instability of the mode pattern as energy is propagated down the line and particularly when the circular wave-guide is bent. This may be required for example in an installation where a signal generator or a receiver is connected to a distant antenna by the wave-guide, with intervening structural members to be avoided by the wave-guide. An object of the present invention is to enable use of circular waveguides where a bend is required. In achieving this object I transform a length of circular wave-guide into a plurality of rectangular wave-guides, which rectangular waveguides can be curved through desired angles. The novel construction thus incorporates a pair of cylindrical guides angularly related and interconnected by means of a curved length of rectangular wave-guide, the latter preferably including plural parallel paths.

In effecting the transformation between cylindrical and rectangular wave-guides there is the further problem of avoiding discontinuity that might cause troublesome reflections and mode transformation to undesired modes. I have devised a novel tapered transition for use in each case where a circular wave-guide joins a rectangular waveguide or multiple rectangular wave-guides.

In another aspect, the present invention is directed to a mode-changing construction for circular wave-guides, which is useful at places where a bend in the circular wave-guide is normally required, and is also useful even where straight lengths of circular wave-guides are used. In this connection the circular wave-guide is connected to paired rectangular wave-guides, preferably with reflectionless tapered transitions, and again converted into a single circular wave-guide. By introducing a phase change in one of the paired rectangular wave-guides as by a dielectric filling, a supplied wave of mode TEoi can be converted to TE11, or the reverse.

The invention will be better understood, together with further objects and features of novelty, from the following detailed disclosure. In the accompanying drawings:

Fig. 1 is a lateral elevation, with a portion broken away, of a construction for achieving a right-angled bend in a circular wave-guide;

Fig. 1A is a view of certain elements in Fig. l, tipped forward for better display of the contours;

Fig. 2 is a sectional view along the line 2-2 in Fig. 1;

Fig. 3 is a transverse section of a circular wave-guide showing the electric field in the TEor mode; and

Fig. 4 is an illustration of the electric field emerging from the tapered transition into the dual rectangular waveguide connector in Figs. 1 and 2;

Fig. 5 illustrates the electric field lines of the T1311 mode of propagation in a cylindrical wave-guide; and

Fig. 6 is a view like Fig. 2 illustrating dielectric filling in one of the paired rectangular paths.

In Figs. 1 and 2 circular wave-guides 10 and 12 of metal tubing are shown at right angles to each other joined by a brass connector 14 embodying a pair of rectangular wave-guides 16 and 18, which are curved about an axis perpendicular to the plane common to the axes of the circular wave-guides. The rectangular wave-guides are separated by a dividing wall 15 which is flat and which forms the boundaries for short sides 16a and 18a of the wave-guides 16 and 18. The long boundaries 16b and 2,706,278 Patented Apr. 12, 1955 18b are curved so as to direct the propagation in line with guides 10 and 12.

Between each circular wave-guide and connector 14 is a tapered transition intended to minimize discontinuity that may cause troublesome reflections and undesired mode transformation. The transition in wave-guide 10 includes a septum 20 formed with an edge 22 of gradually reduced thickness and made up, in this instance, of a pair of metal plates backed against each other. Septum 20 is an extension of wall 15 between the rectangular waveguides 16 and 18. The field propagated along the circular wave-guide is thus divided into two substantially semicircular portions. For smoothly converting the semi-circular fields thus obtained into the transverse electric field of the rectangular wave-guide illustrated in Fig. 4, I have provided a pair of pieces 26 and 28, conductive faces 30 and 32 of which (see also Fig. 1A) have a double exponential taper tangent to both the rectangular conductive boundaries and to septum 20. On the side of septum 20 opposite tapers 26 and 28 is a like pair of tapers 26a and 28a. Each taper 26 is mirror-symmetrical with taper 26a, and with taper 28, and taper 28a, is, in turn, mirror-symmetrical in respect to tapers 26a and 28.

The transition between circular wave-guide 12 and rectangular connector 14 similarly includes a septum and tapers, which are all identified with primed numerals corresponding to those identifying portions in the transition between cylinder 10 and rectangular connector 14.

The bend in the circular wave-guide afforded by connector 14 containing rectangular wave-guides 16 and 18 is effective to change the direction of propagation along either circular guide 10 or 12 to the other while preserving the same mode of propagation. Thus, if the TEM mode of Fig. 3 is introduced into guide 12, it will appear at the input edge of rectangular connector 14 as shown in Fig. 4, and will emerge in this TEoi mode in circular guide 10. This is because the geometry and the electrical length of the two rectangular propagation paths are alike.

The effective or electrical length of travel can be changed, however, by inserting dielectric material into one of the guides 16 or 18 as at 34 in Fig. 6 and the desired phasing can be established in several other ways. If the phase change in the two rectangular waves differs by the unit will transform from the TEoi mode in one circular wave-guide as shown in Fig. 3 to the TEll mode in the other as shown in Fig. 5 or vice versa. The actual lengths of the rectangular sections of wave-guides are not critical for the E-plane bend as long as they are equal in the case where there is to be no transformation and differ by half a wave-length where complete mode conversion is desired. If the difference in electrical length between the two wave-guides is between zero and half a wavelength, the result will be a transfer from the TEM mode on one side to a mixture of TEM and TEn modes on the other side of the bend.

The bend of guides 16 and 18 described is in the E-plane. (The plane of a bend is the plane containing the longitudinal axis of the wave-guide. The plane can be parallel with all E-lines or all H-lines, and the bend is then said to be in the E-plane, or the H-plane, respectively.) The bend could otherwise be made in the H- plane, provided that care is taken to make the relative electrical lengths of the two paths appropriate in relation to the wave-length transmitted and in relation to each other, for the H-plane bend can be used to effect mode transformation without dielectric filling in any of the rectangular guides and where they are of proper length.

By making the exponential tapers any number of halfwavelengths long, impedance match is obtained. If the exponential tapers are gradual, this device is useful in ice large sizes of circular wave-guides where the circular feasible to transform between a circular wave-guide and a p pair of rectangular wave-guides extending not endwise but along a diameter of the circular wave-guide. Consequently the appended claims should be interpreted broadly, as may be consistent with the spirit and scope of the invention.

What I claim is:

l. A wave-guide construction comprising a first circular wave-guide, a second circular wave-guide of equal radius angled in relation to the first wave-guide, a connector between said circular wave-guides having a matched pair of parallel rectangular wave-guides curved so as to merge with said circular wave-guides, the longer sides of each rectangular wave-guide being only slightly shorter than the radius of the circular wave-guides, one of the shorter sides of each rectangular wave-guide utilizing a common wall within said connector, said wall having axial extensions centered in both circular wave-guides, and a symmetrical pair or tapered elements at both sides of each extension proportioned to form double logarithmic curves tangent to the wide sides of the rectangular wave-guides and to said axial extensions centered in the circular waveguides, said extensions being tapered therebeyond to provide passages merging smoothly into said circular waveguides.

2. A pair of like circular wave-guides angled in relation to each other and joined by a connector having a pair of rectangular wave-guide passages curved and directed endwise into said circular wave-guides, and a tapered transition gradually enlarging the wave-guide crosssection from a minimum at each rectangular wave-guide passage and merging smoothly into a semi-circular maximum at the respective circular wave-guide.

3. A wave-guide construction according to claim 2 wherein said rectangular wave-guides are of equal electrical length and of like geometry.

4. A wave-guide construction according to claim 2 wherein said rectangular wave-guide passages are of like geometry and wherein one rectangular passage contains a dielectric medium to extend the effective electric length of said wave-guide one half wavelength at a chosen frequency, thereby to effect a conversion of modes in said circular wave-guides between the TEoi mode and the TEu mode.

5. A wave-guide construction comprising a pair of circular wave-guides of equal diameter inter-connected by paired rectangular wave-guides of electrical lengths differing by any odd number of half wave-lengths, the long dimensions of the rectangular wave-guides extending in opposite directions.

6. A wave-guide construction comprising a pair of circular wave-guides arranged with their axes intersecting and paired curved rectangular wave-guides inter-connecting said circular wave-guides.

7. A wave-guide construction comprising a pair of circular wave-guides and at least one curved rectangular wave-guide directed endwise into said circular waveguides, and transversely extending outward from the respective axes of the circular wave-guide.

8. A wave-guide construction comprising a circular wave-guide and a plurality of curved rectangular waveguides, the rectangular Wave-guides being directed end wise into said circular wave-guide, and a plurality of tapered elements forming a double logarithmic transition enlarging the wave-guide from a rectangular minimum at each wave-guide into a segmental maximum at the circular wave-guide between said rectangular wave-guides and the circular wave-guide.

9. A wave-guide construction comprising a circular wave-guide a pair of rectangular wave-guides having a common dividing wall and joined to said circular waveguide, and a pair of mirror-symmetrical surfaces forming an enlarging transition between opposite walls of each of said rectangular wave-guides of arcuate extent increasing smoothly into approximate semi-circles divided by a diametral plane of said circular wave-guide, said common wall being extended along said diametral plane.

10. A wave-guide construction comprising a circular wave-guide and a rectangular wave-guide opening into said circular wave-guide and extending substantially from the center to the circumference thereof, and a transition from a rectangular minimum at one end adjacent said rectangular wave-guide to a segmented maximum at the opposite end adjacent said circular wave-guide comprising a pair of mirror-symmetrical surfaces whose separation at their outer edges is logarithmically tapered from opposite ends toward the middle thereof.

11. A waveguide construction comprising a circular waveguide, a pair of like rectangular waveguides both arranged for endwise communication to an end of said circular waveguide, the long sides of each of said rectangular waveguides being only slightly shorter than the radius of the circular waveguide, one of the shorter sides of each rectangular waveguide having a wall in common with the other rectangular waveguide, and a transition between said circular waveguide and said rectangular waveguides having a septum extending from said common wall along a diameter of said circular waveguide, and a pair of tapered elements at each side of said septum gradually enlarging the waveguide surfaces that are directly opposite said septum from a minimum equal to the shorter sides of said rectangular waveguides where the rectangular waveguides join the transition to a maximum approximating half-circles adjacent said circular waveguide, said septum being tapered therebeyond to merge smoothly into said circular waveguide.

12. A pair of like circular waveguides angled in relation to each other and joined by a connector having a pair of rectangular waveguide passages curved and directed endwise toward said circular Waveguides, and a tapered transition between each end of each rectangular waveguide passage and the respective circular waveguide, wherein the radially outermost waveguide surfaces are limited adjacent the ends of the rectangular waveguides to the extent of the adjoining rectangular waveguide wall and said surfaces are enlarged along the transition toward the circular waveguide to the extent of approximate halfcircles adjacent the circular waveguide.

13. A Waveguide construction according to claim 2 wherein said rectangular waveguide passages differ in effective electric length by one-half wave-length at a chosen frequency thereby to effect a conversion of modes in said circular waveguides between the TE01 mode and the T11 mode.

14. A waveguide construction comprising a pair of circular waveguides of equal diameter interconnected by a pair of rectangular waveguides, the longer transverse dimensions of the rectangular waveguide being disposed about opposite radii of the circular waveguides at the respective junctions therewith and being curved about an axis parallel to those radii.

15. A bent waveguide construction including input and output circular Waveguide portions, curved rectangular sections of waveguide between said circular portions operating in the TE10 mode, and progressive transitions between each rectangular waveguide section and each circular waveguide section.

16. A bent waveguide construction including input and output circular waveguide portions, a pair of curved rectangular sections of waveguide between said circular portions operating in the TE10 mode, and progressive transitions between each rectangular waveguide section and each circular waveguide portion, one of said rectangular waveguide sections embodying a phase shifting construction different from that of the other rectangular waveguide section so as to transform the mode of propagation in the input circular waveguide portion from TEOI to the TEu mode in the output circular waveguide portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,129,669 Bowen Sept. 13, 1938 2,129,714 Southworth Sept. 13, 1938 2,439,285 Clapp Apr. 6, 1948 FOREIGN PATENTS 222,399 Switzerland Oct. 1, 1942 

